The present invention relates to a printing press with a varnish unit for coating the lower surface of a sheet with varnish.
As a printing press of this type, one disclosed in Japanese Patent Laid-Open No. 3-190735 is known. The printing press disclosed in this reference has a sheet feed unit for feeding sheets one by one, a coater unit for coating the lower surface of a fed sheet with varnish, and a printing unit for printing an image or the like on the upper surface of the sheet. The coater unit has a coating impression cylinder in contact with an impression cylinder arranged in the printing unit, a coater cylinder in contact with the coating impression cylinder, a coating supply unit for supplying a coating material to the coater cylinder, and a dryer unit for drying varnish applied to the lower surface of the sheet.
In this arrangement, while the sheet fed from the sheet feed unit passes between the coating impression cylinder and coater cylinder, its lower surface is coated with varnish. Then, varnish is dried by the dryer unit. After that, the sheet gripped by the gripper unit of the impression cylinder of the printing unit is transported, by rotation of the impression cylinder, while its lower surface is in contact with the surface of the impression cylinder, and the upper surface of the sheet is printed while the sheet passes between the impression cylinder and a blanket cylinder.
In the conventional printing press described above, a dryer for drying the varnish is comprised of an infrared heater and a fan for blowing off air heated by the infrared heater. However, a dryer with high drying power cannot be installed because of the problem of the space where it is to be installed, the varnish is not dried sufficiently due to the adverse influence of heat to the printing press body, and the like, depending on the type and coating amount of aqueous varnish applied to the sheet. If the varnish is not dried, undried varnish sometimes attaches to the surface of the impression cylinder of the printing unit while the sheet is transferred from the coating impression cylinder to the impression cylinder of the printing unit. The varnish attaching to the surface of the impression cylinder hardens, and undried varnish is repeatedly deposited on it to form a lump of varnish. This damages the sheet transferred to the impression cylinder of the printing unit.
An impression cylinder plate is mounted on the circumferential surface of each of the coating impression cylinder and the impression cylinder of the printing unit in order to prevent damage to the cylinders. Although the impression cylinder plates with surface precision almost equal to that of the surfaces of the cylinders are plated for rust prevention, undried varnish cannot be prevented from attaching to them.
It is an object of the present invention to provide a printing press in which damage to a sheet on the surface of an impression cylinder is prevented.
In order to achieve the above object, according to the present invention, there is provided a printing press comprising a first cylinder with sheet holding means for holding a sheet-like object and rotatably supported, a varnish unit for supplying varnish to the sheet-like object held by the first cylinder, and a second cylinder in contact with the first cylinder and having second sheet holding means for receiving the sheet-like object held by the first cylinder, the sheet-like object held by the second sheet holding means being transported such that a varnish-coated surface thereof opposes a surface of the second cylinder, wherein a fluorine-contained polymer layer is formed on a surface of the second cylinder which is in contact with the varnish-coated surface of the sheet-like object.